# Tag Info

40

What you are calling a focal point is the end of the umbra, the point at which the umbra changes to the antumbra. In a total solar eclipse, that point is below rather than above the surface of the Earth. An annular eclipse occurs when that point is above the surface of the Earth. The Moon appears to be smaller than the Sun, leaving an unbroken ring of the ...

30

I did see the Venus transit before the Sun in 2004. I used no telescope, but of course I used proper solar eclipse glasses to protect my eyes. The black circle was small but clearly visible. But Mercury is much smaller, the transit is not visible without a telescope. See Wikipedia. Here an image of a Venus transit: Here the much smaller Mercury: The ...

27

I'll use the atmosphere as my big natural lens. So I'll watch the upcoming mercury transit at the sunset time where the sun looks bigger than usual. While the Sun and Moon might seem larger at the horizon, their angular size doesn't get larger. It's an optical illusion. Will this make the black dot of mercury bigger or big enough to be obviously seen by ...

19

During a sunset, the Sun is lower in the sky than during most of the day - much lower. Therefore, light from the Sun travels through about 120 miles of dense atmosphere, compared to the roughly 2 miles it travels through from straight up. Here's a rough sketch (not to scale) to demonstrate this. It is clear that $B>A$: Light scatters in the atmosphere; ...

15

As the Moon's eccentric orbit around the Earth brings it nearer and farther, current solar eclipses can be total or annular. A few in between are hybrid eclipses: total along the midday part of the path, and annular near the sunrise or sunset end. This happens mostly due to the Earth's surface curvature and partly due to the Moon's orbital eccentricity. ...

12

The NASA sites have some very useful resources for this I will list them below: Lunar Eclipses This Link has an index for all lunar eclipses from -1999 to +3000, predominantly a statistics page but also has this page that contains how to calculate when lunar eclipses are. There is more than one formula depending on which time frame you are trying to look ...

10

One thing to double check is if you can see stars easily at night from the same location. If there are city lights nearby, combined with humidity or dust you can have a bright sky due to terrestrial effects. Another thing to consider is the time needed for dark adaptation. If you walk from a brightly lit room out under a dark sky, you can't see many stars ...

9

Solar and lunar eclipses occur about equally often - between two and four times per year. However, when you do not intentionally travel around the world chasing solar eclipses, you are more likely to observe more lunar eclipses. The reason is that solar eclipses can only be observed from a comparatively small area while lunar eclipses can be observed from ...

9

Calculation of solar eclipses can be done using Besselian elements. The basic idea is to compute the motion of the Moon's shadow on a plane that crosses the Earth's center. Then, the shadow cone of the Moon can be projected on the Earth surface. The Besselian elements are the following: X and Y: the coordinates of the center of the shadow in the ...

8

If it's not safe to look at the sun's reflection in the water normally then it's no safer during an eclipse because even if 1% of the sun is showing this is more than enough light to seriously damage your eyes. The best way to view the sun, if you haven't ordered your eclipse glasses yet, is to poke a hole in a piece of paper and project an image of the sun ...

8

It seems that the station has, in fact, given out extremely dangerous advice - simply because it was poorly phrased. Viewing a solar eclipse is incredibly dangerous - mostly under circumstances where you're looking towards the Sun. As Wikipedia warns, Looking directly at the photosphere of the Sun (the bright disk of the Sun itself), even for just a few ...

7

The beads of bright light can be seen thanks to the Moons rugged topography. They're called Baily's beads in honor of an English astronomer who explained the phenomenon, Francis Baily. In the photograph you posted, you can also see Solar prominences. It's plasma ejected into the corona. Its temperature is lower than that of the coronal plasma and it emits ...

6

A hybrid eclipse is one in which it is a total eclipse in some places and an annular eclipse is seen in other places. As you may know, a total eclipse is one in which the moon completely covers the disc of the Sun; this allows the solar corona to be seen. Usually the central disc of the Sun is so bright that the corona cannot be seen. An annular eclipse ...

6

There is no antumbra in this image. An antumbra only exists when the moon is further from the Earth than in that image, so that the moon appears smaller in the sky than the sun. In that case, when the moon is perfectly aligned with sun, a ring of sun is visible behind the moon. The region in which the ring is visible is called the antumbra. In the image, ...

6

The Sun is the same as ever. It's just that people tend to stare at it for long times during the eclipse. A quick glance doesn't do much damage, but prolonged staring could be bad. Those who see the phase of totality have an additional risk. After the Sun goes completely dark, and it then finally shows up again, some people feel compelled to keep watching ...

6

I wanted to ask this question even though I realized the correct geometry in the middle of typing it. So I will answer this myself. First of all, the sub-lunar point never exceeds 28.545 N/S. If you're standing at the sub-lunar point, the Moon will be directly overhead. The Moon never wanders outside this latitude bracket. But that does not mean the Moon's ...

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The reason is because the moon moves much faster (in terms of angle per day) than the sun. In fact it moves on average 12.5 degrees per day, and all in the same direction. Given that the sun is only about 0.5 degrees in diameter, it doesn't take long for the moon to overtake it, and once it's past it doesn't go backwards.

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The only potentially valid way to cause a long-lasting eclipse that I can think of is to have your moon orbit at the planet's L1 Lagrange point between the planet and the star (and the moon has to be the right size). If it had just the right orbit and was the right size, it could then cause a long-lasting eclipse. Note I'm not saying permanent because such a ...

6

Eric Pauer, who produced the chart, has an interesting web site that covers this eclipse. It is evident that the weather was not great at the time of the eclipse, with intermittent cloud, and it will have been passing clouds that caused the variations in intensity. You can see the evidence from this page http://www.pauerhome.com/eclipse/eclipse99/1contact/...

6

I will take a stab at it. Assuming the last eclipse happens when the moon is at perigee and the earth is at aphelion. the moon's perigee is increasing by 4 cm per year, the earth's aphelion does not change with time, the sun and the moon are perfect spheres, the radius of the sun and moon don't change, and a total eclipse occurs when \$r_{\mathrm{sun}}/d_{\...

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Short answer: No, it could not. The moon already has little enough mass relative to the earth so that its orbital period is not much shorter than a satellite with negligible mass. So, any object at about the distance of the moon would take around a month. If the object really had negligible mass it would be moving a little slower than the moon, so let's be ...

5

Yes, total Solar eclipses can occur anywhere. On any given place, they occur roughly every 400 years, on average. If you take a look on the picture below (from Wikipedia), you'll see that within the last one thousand year, almost every place on Earth has experienced a total Solar eclipse. The places that haven't experienced one have no special latitude or ...

5

The answer by @mso is very good. Another contributing factor is the exposure time of the camera on New Horizons. The amount of light reflecting from Pluto is greater than that from the background stars. As a result the exposure time is set to achieve a good image for the desired target and detail required. Over the integration time the amount of light ...

5

Relative to the Sun, stars, and Earth's shadow, the Moon always appears to move from west to east. How this looks relative to the horizon depends on your latitude and time of day. If a solar eclipse occurs in the middle of the day, the Moon appears to move from right to left if you're in a northern latitude, or from left to right if you're in a southern ...

5

As Wayfaring Stranger's answer says, during a lunar eclipse seen from Earth, an observer on the Moon would see a solar eclipse. Earth is about 4 times the apparent diameter of the Sun. You can see a photo of such an eclipse, taken by Japan's Kaguya spacecraft in lunar orbit, here. During a solar eclipse seen from Earth, an observer on the Moon would see the ...

5

Projection is a safe way to view the partial phase of the eclipse. A pinhole produces a small image of the sun, but doesn't require any special equipment. A larger image can be obtained by projecting through a telescope: Point the scope at the sun, but never look down a scope that is pointing anywhere near the sun, neither look along the tube. Use its ...

5

At 99% the sun will be reduced to a small sliver. There are simulations on the internet. It will become very notably darker. However, the sun is 400000 times brighter than the full moon, so 1% of the Sun is still 4000 times brighter than the Moon, and so no corona will be visible. You can still damage you eye looking at that sliver. Since the centre of ...

5

As seen in this comment, normal daylight is around 100,000 lux, but 10,000 lux is still considered daylight. So, unless you're getting close to 99%, it will still be fairly light outside.

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The real reason is that the human eye is not a linear sensor. A 10x decrease in illumination does not produce a 10x reduction in your perception of light, but more like a 2x reduction at most. So yes, during the 90% phase of a partial eclipse, the level of illumination is massively reduced. You could check it with a device that could measure ambient light, ...

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